Texan voters under 30 have already seen a 477-percent increase from the 2014 midterm elections.

Data shows that young people are voting early in troves in Texas, where progressive Democrat Beto O'Rourke is hoping to overthrow incumbent Republican Senator Ted Cruz in the upcoming midterm vote.

Upwards of 332,000 Texans between the ages of 18 and 29 took part in early voting, marking a 477 percent increase from the 2014 midterm elections, according to a survey by the data company Target Smart.

With more than 214,000 people voting for the first time, Target Smart's data also found that the turnout of African American and Latino voters more than doubled since the 2014 midterm.

Donald Trump won Texas, traditionally a Republican stronghold, by nine percentage points during the November 2016 presidential elections, when he defeated Democratic candidate Hillary Clinton.

An October 28-30 poll by Emerson College found that Cruz had a narrow lead over O'Rourke, putting the Republican incumbent at 50 percent support and his challenger at 47 percent.

The website FiveThirtyEight estimates that O'Rourke only has a 20 percent chance of winning.

But O'Rourke, who has been tipped as a possible presidential hopeful in 2020, has consistently claimed that the polls are underestimating the Latino vote.

Latino voters leaning Democrat

A recent study, published last month by Texas-based Jolt Initiative, appears to support O'Rourke's claim, concluding that 32 percent of Latino interviewees prefer the Democrats, while only 13 percent support the Republicans.

Titled We Are Texas: An Analysis of Young Latino Voters in the Lone Star State, the report predicts that Latinos will constitute the state's largest ethnic group by 2022.

Around half a million Latino non-citizens in Texas qualify for US citizenship.

"With some of the lowest voter registration and participation rates in the country, Texas faces real barriers to building a healthy and strong democracy," it states, explaining that "the strength of our democracy will be determined in large part by engaging young Latinos".

With Trump escalating anti-immigrant rhetoric and sending troops to the border in response to a US-bound caravan of Central American migrants and refugees, an O'Rourke victory would be seen as a strong rebuke to the president's immigration agenda.

The midterm elections will decide all 435 seats in the House of Representatives, 35 seats in the Senate and 39 state and territorial governorships.